Convergence and Divergence 107 



us must somehow carry on certain common activities. The 

 striking fact is that similar results, so far as concerns main- 

 taining life, are obtained in so many different ways. 



Convergence and Divergence 



It has been pointed out that adaptations may be brought 

 about in two different ways — if we disregard the theory of 

 special creation. 



I. Unrelated species, having to live under similar con- 

 ditions, come to assume similarities. Thus the whale, a mam- 



FiG. 32. Diggers from Different Sources 



The front legs of the mole cricket, an insect, and the front legs of the mole, 

 a mammal, show striking superficial resemblances, and these are related to the 

 similar ways in which the two animals use these structures. 



mal, the squid, a mollusc, the fossil ichtyosaur, a reptile, 

 present an outward appearance suggesting a "fish"; there 

 is here such an adaptation of form to conditions of living 

 that animals of unrelated stocks resemble one another (Fig. 

 31). Insects belonging to distinct orders assume similari- 

 ties of color or even of form — as certain katydids (orthop- 

 tera) and certain "bugs" (hemiptera) — because of their 

 supposed protective advantage; and green snakes and green 

 lizards are just as green as green katydids. 



A remarkable instance is seen in the resemblance be- 

 tween the front feet of the mole, a ground-burrowing mam- 

 mal, and the front legs of the mole cricket, an insect with 

 somewhat similar habits (Fig. 32) . Nobody giving attention 



